An in vitro preparation of nerve and muscle which is capable of forming functional synapses has been developed. Processes growing from a nerve explant contact myotubes and form synapses, sometimes in less less than a day. Recordings from the muscle fibers often reveal spontaneous synaptic potentials; these potentials can be evoked by stimulation of nerve processes. Muscle fibers receive multiple innvervation, but apparently not all nerve processes make functional synapses with the muscles they contact.